CLIMATE. 



CLIMATE. 



HI 



U equally certain that it depend* mainly nn the hygrometrical state ol 

 the atmosphere, which again in a great degree depend* u thf wind*. 



. the time of Franklin, the attention of observers hoc been 

 drawn U> the effects which the temperature of one country has on that 

 tiguous countries. In calm weather that effect is probably BO 

 mall u not to be perceptible. But whenever a wind is storing, i< 

 bring! the colder or warmer air from one country to the other, and 

 thu* lowers or raises the temperature of that country to which it 

 blows. This effect is very perceptible c.n the eastern shores of 

 England, with respect to the easterly wind-. In the latter jm 

 spring or early in summer, these winds, before they reach 1 

 pa*s over the still chilled and dump surface of toe great plain ol 

 Northern Germany, ami blight the already advanced vegetation i .'. 

 eastern counties. On the contrary, in autumn the same wii: 

 i.v.-r a sandy soil, which during the summer has acquired a consider- 

 able degree of heat, and the air brought over liy them U warm enough 

 to raise the thermometer several degrees. A still more remarkable 

 instance is mentioned by Pcrppig, in his ' Travels through Chil 

 Ac. In the southern districts of Chile, the eastern winds, called there 

 Ion Fuelches, when they blow in spring (September) are so cold that 

 they depress the thermometer in a short time 15 or 18 degrees ; but 

 towards the end of the summer (February) they raise it nearly as 

 tuuch. He attributes naturally enough the first effect to the chain o) 

 the Andes being covered with deep snow during the spring, and the 

 second to the high temperature to which the air upon the sandy plains 

 ol the Pampas of Buenog Ayres is raised during the summer months. 



Considering the great effect which the temperature of countries 

 contiguous to one another exercises on their respective climates, we 

 may presume that a similar effect is produced by seas similarly 

 situated. This has been long ago shown by the observations made on 

 the regular change of the land and sea breezes in warm countries, and 

 by the explanation of this phenomenon, which is obvious and simple. 

 But it hu only been recently ascertained, that the proportion between 

 the temperature of the sea-water and the atmosphere above it is not 

 everywhere the same, but that in some parts the sea-water is warmer 

 than in others under the same latitude. Now the temperature of the 

 water must in some degree affect the temperature of the atmosphere, 

 and this atmosphere, when brought into contact with the air of the 

 land by the winds, must produce a change in its temperature. This 

 consideration may sufficiently explain why the countries round the 

 Mediterranean enjoy a much milder climate than all others placed 

 miiliT the same parallel. It is now ascertained that the temperature 

 of the water of the Mediterranean Sea is from 4 to 5 higher than 

 that of the Atlantic in the same parallel. This may perhaps lead us to 

 the explanation of the greatest anomaly of climate which exists on the 

 globe we allude to the great difference of temperature existing between 

 the western countries of Europe and all the other countries of the globe 

 ying in the same parallel. 



Those who had the first opportunity of observing the difference in 

 temperature between western Europe and the eastern coasts of North 

 America were natives of western Europe, and of course they considered 

 the climate of their own countries as constituting the rule, and that of 

 North America as the exception. They accordingly attempted to 

 explain this phenomenon by a reference to some peculiarities which 

 characterise North America as a continent, such as the increase of its 

 breadth towards the poles, the stretching out of the continent so far 

 to the north, iu large rivers and lakes, &c. But when the temperature 

 of Asia and the eastern countries of Europe was ascertained by obser- 

 vation, it appeared that their temperature differed as much, and in many 

 places still more, from that of the western countries of Europe than 

 North America does. The climate of America may therefore bo con- 

 sidered as the rule, and that of Europe the exception. Still the 

 question remain*, to what peculiar circumstance it is owing that the 

 temperature of Western Europe differs from that of America and the 

 countries lying farther east in the same latitude by 8 or 10. 



Wo venture to offer an opinion that the Gulf Stream is the most 

 active, if not the only, cause in producing this difference. This re- 

 markable current stretches across the Atlantic between Cape Hatteras, 

 in North America (35 N. lat), and the Azores, forming nearly in the 

 middle of the Northern Atlantic a lake of warm water, which, accord- 

 ing to the calculations of Major Rennell, is not inferior to the Mediter- 

 ranean in extent. The temperature of its water is from 8 to 10 

 higher than that of the surrounding sea. The temperature of the 

 superincumbent air is likewise several degrees higher than it is farther 

 to the west and south, but less so when compared with those portions 

 of the Atlantic which lie farther to the east and north-east. \\- think 

 that this last difference is due to the strong gales which are nlmont 

 continually experienced in navigating the Clulf Stream, but more 

 especially on it* borders; they blow most frequently from the south- 

 west and west. Winds blowing from these quarters are by far the 

 mart prevalent in the Northern Atlantic, and it is observed that even 

 on the coast of Western Europe they still preserve the character im- 

 pnsMd upon them by the gale* of the Gulf Stream. They do not 

 blow equably like the other wind*, but in abrupt gust*, with short 

 intervals of calm. These winds appear to waft the warmer air of the 

 Oulf Stream over the whole of the coast* of Western Europe from Cape 

 KinisUrra a* far as North Cap* ; they even penetrate through the wide 

 (ate between the Han mountain* and the Scandinavian range* into 



tho recess of the Baltic, and their effects extend to the very plains ol 



..': tliry .:M- i prevailing north-eastern winds and 



stopped. All the countries within the range of these winds 

 a much more favourable climate than those to which they do not 

 extend. 



It may here be objected, that as tin i ;.ili Stream approaches inm-h 

 nearer the coast of North America than tli.it of Kurope, and as the 

 t.-nii-nitiire of itx water i* also highest there, such an effect as is here 

 described should rather apply to the New than to the Old <'<n.- 

 But, in the first place, the Oulf Stream along the coast of America is 

 of comparatively inconsiderable width, being opposite Charleston only 

 from 60 to 63 miles across : and, secondly, its waters in their 

 course along that coast lose very little of their temperature. At Cape 

 Hatteras, after a course of 900 miles, the stream ha* only lost 8 

 of warmth. Kroin this point it turns to the east, and the decrease of 

 temperature begins to be somewhat greater. Yet even opposite the 

 great bank of Newfoundland, after a course of 1800 miles through 15 

 of latitude, its waters have lost only 5 Fahr. of warmth, anil the 

 temperature in this part is from 8 to 10 above that of the a. I 

 ee;us. The decrease of temperature begins to be most consid 

 about the middle of the Atlantic. Now, when we consider that on 

 the eastern coasts of North America likewise the western and 

 western winds prevail, it follows that by far the greatest portion of the 

 warm air derived from the evaporation of the Gulf Stream must 

 to those countries which lie to the leeward of these winds. Th< 

 "t North America, however, to the east of the Appalachian range, 

 seem also to feel in some degree the heated air of the Gulf Stream ; 

 since it has been proved by Darby that they have n re by 



degrees higher than the parts in the same latitude to the west 

 of that range. 



Another remarkable difference in temperature occurs in the countries 

 which form the most southern part of the American continent. HIIIII- 

 boldt has compared a considerable number of observation-. from which 

 it appears that south of 46 the mean temperature of South \ , 

 is from 12 to 18 lower than that of those parts which lie in tin- same 

 latitude iu other meridians. North of 48 8. lat this difli-i 

 considerable, but it gradually diminishes as we approach the i 

 At about 80 it seems to disappear entirely. The greater cold 

 antarctic regions had been recognised before. It was conjectured by 

 Captain Cook to be due to the existence of a large tract 

 tween 70 S. lat. and the polo. This was singularly 

 investigations of Sir James C. Ross in 1841, who found V; 

 extending from 71 to 79 S. Int., skirted by a great barrier 

 and the land itself, ranging in altitude from 4000 to 14,000 feet, 

 entirely covered with snow. 



Many persona suppose that tho peculiar form oi Smith America, 

 which narrows towards the south, and stretches out in the form 

 acute angle, may be sufficient to explain thi- phenomenon; but this 

 diminution of the surface of the land should rather have . 



.I tho true cause we have no doubt is to be found in tho 

 last stated. 



There are other circumstances, besides those enumerated, which 

 affect the general temperature, but their influence is confined to sm ill 

 bracts. Thus the temperature of some places is consi.l. r.il.lx i-.ii 

 lowered from their being situated on the southern or northern declivity 

 of a high range, or in a narrow valley, or from their bring entirely or 

 in a great part surrounded by water. Even the existence of 

 forests has some influence on the temperature of contiguous ,. 

 But as the influence of such circumstances is local, it may be mill 

 liere to indicate it. 



The circumstances which tend to increase or to depress the general 

 temperature of a country being so numerous, and their <t! 

 hieing which several of them often co-operate) being in some instances 

 very great, it often happens that the actual temperature of a country 

 liffers considerably from that which might IKJ inferred from the 

 atitudc in which it lies. To show therefore what countries, situated 

 mdiT different parallels, have an equal or nearly equal temperature, 

 the isothermal lines, or lines of equal temperature, have been 



dliced. [ItOTRKRMAL LlNES.] 



The second chief constituent of climate, the moisture of the air, 

 appears under the form of rain, vapour, fog, mid dew. \Ve shall limit 

 nir observations to rain, in this article. 



There are extensive tracts of this globe on which a drop of rain is never 

 mown to fall, or only at intervals of many years, and then only in 

 piantitiea. These countries ye always found neat sometimes 



xtending on both sides of these circles, but often inly on tl. 

 awards the poles, which circumstance is probably to be ascrilir.l i .. 

 ocal iieculiarities. These countries may be said tn run lil.- 

 .mud the globe, dividing the countries on each side of tho e<|uin 

 lino from the temperate zone, as Posidonins very correctly stated. It 

 is only where mountain-ranges exist, that these belts of rainless regions 

 are interrupted. Beginning with the OM Continent, we find in Africa. " 

 the Sahara or Great Desert, on the southern borders of which i!, 



ae at about 16 N. lat. and on the north begin at about 28. 

 Proceeding farther east, the southern rains cease in the c. 

 Jie banks of the Nile between 18 and 19, and the northern 

 between 27* and 28. Pawing the Gulf of Arabia we find 1 1 

 or low coast of Arabia, which is destitute of rains ; but we do not yet 



